This invention relates to an actuator device. In particular, the actuator device of this invention is a permanent magnet actuator mechanism. In operation, a first permanent magnet member co-acts with a second permanent magnet member in a master/slave relationship. The permanent magnet members are positioned with the magnet members in mutual magnetic repulsion wherein displacement of one of the permanent magnet members automatically effects opposite displacement of the other of the permanent magnet members.
The use of permanent magnet members in mutual repulsion has heretofore generally been avoided because of the problems with demagnetization of the magnets. However, with the discovery of new powerful magnetic materials that resist demagnetization, novel actuator mechanisms with permanent magnets in mutual repulsion may now be devised.
In many mechanical and electro-mechanical systems it is desirable to displace one element by displacement of another element without direct contact of the displaced element by the displacing element. For example, displacement of a valve spool in a fluid conduit by a displacement of an actuating element, external to the conduit has advantages when the external element is not physically connected to the valve spool. The elimination of seals, valve stems and other components commonly employed in valve assemblies of the poppet type, avoids the potential for leaking and/or contaminating the fluid in the conduit.
It is a principal object of this invention to effect the translocation of one element by the translocation of a controlled element using magnetic repulsion.
It is an additional object of this invention to accomplish the translocation of the target element by actuation of the controlled element without the controlled element directly contacting the target element.
It is a further object of this invention to allow translocation of the target element even where there is a barrier separating the translocated element from the controlled element.
It is an important object of this invention in many applications to provide a reversible translocation of the target or slave element by a reversible translocation of the controlled or master element.
As an additional object, in the reversible translocations of the master and slave elements, the elements adopt a fixed state wherein a bistable actuator is formed. In the reversible fixed states of the master and slave elements no energy is required to maintain the elements in their switchable fixed states.
The invented permanent magnet actuating mechanism includes permanent magnet members acting in mutual repulsion which effect relative opposite displacements of the magnet members when actuation of one member is initiated by an external force. The translocation of the magnet members enables the magnet actuating device to function as a switching device, in particular, a bistable switching device. In other applications the magnet actuating mechanism operates as a reciprocal displacement device wherein displacement of one magnet member in one direction effects displacement of the other magnet member in the opposite direction.
The relative displacement of the magnet members, enables the permanent magnet actuating mechanism to have application in a variety of devices in addition to the valving and switching devices mentioned. These applications include, but are not limited to, piston mechanisms, vibrators, clamping devices and other systems where reciprocal displacements and reversible translocations are desired.
In view of the objects of this invention and the attributes of the mechanism for implementation, one skilled in the art will be able to modify the structure and tailor the parameters of operation to suit a variety of applications of the type suggested.
The permanent magnet actuator mechanism of this invention comprises an assembly of two permanent magnet members in a framework or containment structure that maintains and limits the relative positioning of the magnet members during displacements. Each of the permanent magnet members in the simplest embodiment comprises a single permanent magnet element. The two permanent magnet elements are positioned in the framework for limited reciprocal displacements and are juxtaposed with magnetic fields in mutual repulsion.
One of the permanent magnet elements is the master element and is arranged in the framework for a relative displacement greater than the other element, which becomes the slave element. The displacement of the master element from one of its limit positions to the other, abruptly causes the opposite displacement of the slave element from one limit position to the other. The master element and the slave element are then each held in the switched position by the mutual repulsion forces of the magnet elements.
In the preferred embodiments described, the magnet members are each an assembly of magnet elements and pole elements that are arranged to optimize one or more selected variables of operation for the application desired. In addition, the permanent magnet actuator mechanism in one embodiment includes spring elements associated with the master permanent magnet member for modifying the forces required to move the master magnet member over the distance of displacement.
It is to be understood that in a permanent magnet actuator mechanism without springs or other attenuating means, the typical force curve for a symmetrical system is approximately sinusoidal. The forced displacement of the master magnet member initially meets peak resistance, which drops to zero at a neutral position in between the terminal positions of the master magnet member, and at this point the slave member automatically switches position, becomes negative, being force driven to the opposite position by the repulsion of the shifted slave member. By appropriate selection and engagement of compression springs, for example, this otherwise lost energy of the displacing master magnet member can be captured as potential energy in the compressed spring element for use in the next translocation of the master member.
The strategic use of springs or other means for assisting actuation, for example, fluid pressure, provides an additional controllable variable in the application of the permanent magnet actuator for different uses. For example, the force curve can be flattened so a small but uniform force applied to the master magnet member throughout the period of displacement effects the shift of the slave magnet member, which is held in its shifted position by a magnetic force of repulsion that may be many magnitudes greater than the external displacement force applied to the master member.
Disclosed in this specification as one useful embodiment is a bistable actuator constructed with two or more coaxial permanent magnets magnetized in the axial direction and spaced so that their magnetic fields are in opposition to one another. The internal magnet, which may be a disc magnet, is free to move axially within limits established by a housing. The internal magnetic provides the output force of the actuator and will normally have one or more rods attached to it which exit the housing. The external magnet, which is preferably a ring magnet, is free to move axially along the outside of the housing. The housing also provides mechanical stops for the external magnets, however, the external magnets are allowed to move further than the internal magnet by an amount that is established by the thickness of the magnet and the range of motion of the internal magnet.
Because the magnetic fields in a typical arrangement are placed so that the north and south poles of the two magnets are oriented in the same direction, the opposing fields will push the internal magnet to one end of its travel while the external magnet will be pushed to the mechanical stop at the other end. This opposing magnetic force is the force that is available from this actuator. To cause the actuator to switch to the other bistable state, a force is applied to the external ring magnets that moves these magnets axially towards the internal magnets which are kept from moving away by their mechanical stop. When the magnetic centerline of the external magnets passes the magnetic centerline of the internal magnets, the internal magnets then experience a force that pushes them in the opposite direction. The internal magnets then move to the other limit of the travel and the external magnets will continue moving in the same direction to the mechanical stop away from the internal magnets. Force is now generated in the opposite direction from before switching.
The driving force for moving the external magnets (and causing the actuator to switch states) can be obtained by many different ways including manual operation, with electric coils or motors, or, by pneumatics or hydraulics. The use of electric coils is a particularly desirable activation method because of the simple direct electrical control that this allows for automatic operations. However, electric coils do not generate as high forces as are available from high strength rare earth magnets. To solve this problem springs can be added to one or both ends of travel of the external magnets. These springs can absorb energy while the mechanism is closing and this energy can be extracted when the mechanism switches back to the original position. The spring energy directly reduces the required activation force allowing high force actuators, while still using small coils which are not ordinarily capable of developing such high forces. The springs also provide a shock absorber function for the switching movement of the external magnets.
Several advantages of this mechanism should be pointed out. First, it is a naturally bistable mechanism which requires no power to generate actuator force. Operation by electric coils is particularly advantageous since the coils can be pulsed to switch states of the bistable actuator mechanism. Power is consumed only during switching operations. No energy is required to maintain the mechanism in either of the switched states. Second, in axial or symmetrical systems the internal magnets are naturally self centering since they are arranged in opposition to the external magnets. Third, the internal actuator can be easily isolated from the external switch mechanism by the housing wall. This is particularly well suited for a positively actuated valve. Fourth, almost any desired force can be generated by either making the magnets bigger in diameter or by increasing length by stacking multiple magnets together in alternating north-south/south-north assemblies or by both means.
Multiple stacks of magnets can use magnetic focusing techniques using iron or radially polarized magnets to increase the coupling strength between the internal and external magnets. Magnet dimensions for maximum coupling force can be calculated for any desired mechanical geometry and magnetic materials. Fifth, by proper spring sizing very little force is needed to get this actuator to switch from one state to the other. Sixth, the actuator can be made to go normally open or normally closed when the power fails by choosing appropriate springs and using activated coil force to hold the external magnets in one position or other. Seventh, the design is naturally compact and easy to construct. The only expensive components are the magnets. Eighth, the visual position of the ring magnets provides a clear indication of switching state of the actuator. This position can be detected by an electronic circuit and reported back to a control mechanism. Ninth, the switching action can be made to happen fast. Tenth, the length of travel of the actuator can be set by choosing the magnet thickness.
A positively driven valve is constructed by using this actuator which can generate a force inside a housing, it creates a valve without the need for a dynamic stem seal as is required by most solenoid valve designs. Eliminating the stem seal eliminates the main leak path of most valves. The valve is a constant volume valve since no volume changes occur with switching. This means that the pressure spikes most valves generate when switching are eliminated. Since the actuator only needs power when it is switching this also eliminates the heating normally generated by solenoid valves. Since such high forces can be generated, valves can be made that go to higher pressure or have bigger flow paths. Valves using this actuator can easily be constructed as a normally open or a normally closed valve with appropriate spring selection. Also, a three way valve which goes from ON-OFF to OFF-ON while passing through the ON-ON state is easily made at very little additional cost over a simple two way ON and OFF valve by putting a flow control element and fluid port on each end of the internal magnetic actuator.